Various energy sources such as radiofrequency (RF) sources, ultrasound sources, and lasers have been developed to coagulate, seal or join together tissue volumes in open and laparoscopic surgeries. One method of tissue sealing relies upon the application of electrical energy to captured tissue to cause thermal effects therein for sealing purposes. Various mono-polar and bi-polar radiofrequency (RF) instruments and jaw structures have been developed for such purposes. In general, the delivery of RF energy to a captured tissue volume elevates the tissue temperature and thereby at least partially denatures proteins in the tissue. In a typical arrangement of a bi-polar radiofrequency (RF) jaw structure, each face of opposing first and second jaw members can include an electrode. RF current can flow across the captured tissue between electrodes in the opposing jaw members, denaturing many of the proteins in the captured tissue. Such proteins, including collagen, can be denatured into a proteinaceous amalgam that intermixes and fuses together as the proteins recombine. As the treated region heals over time, this biological “weld” can be reabsorbed by the body's wound healing process. Another method of tissue sealing relies upon the application of ultrasound energy to tissue captured between jaw members. The application of ultrasound energy to the captured tissue can likewise elevate the temperature of the captured tissue and thereby similarly denature proteins in the tissue.
Performance of tissue sealing surgical instruments can vary based on several factors and the design of such an instrument can be driven by competing desires. For example, the instrument must be capable of sealing the targeted tissue as described above, but surgeons or other users also want to minimize the time necessary to form the seal, as well as the amount of collateral tissue damage due to lateral thermal spread through tissue outside of the jaw members. Applying a high level of energy rapidly can form a seal quickly, but can also result in excess heating of the instrument electrodes via resistive heating or conduction of heat from the tissue into the electrodes. Excessively hot electrodes can begin sticking to tissue and cannot be repositioned without damaging tissue unless they are first allowed to cool for a period of time. Reducing the amount of energy applied to the tissue to address this problem, however, can increase the time to form a seal and can result in greater thermal spread through tissue over that time.
In addition, the particular configuration of the surgical instrument plays a role the management of thermal energy. For example, if an instrument's electrodes are thermally insulated from the jaws and other structure, the time to cool excessively heated electrodes before repositioning can increase significantly. Conversely, if there is good thermal conduction between an electrode and the remainder of the instrument, heat can be more efficiently transferred away from the treatment site, but this can increase the time to form a seal and result in increased thermal spread through adjacent tissue.
Accordingly, there is a need for improved devices and methods for managing thermal energy during tissue sealing operations.